1. Field of the Invention
The present invention relates to an apparatus for detecting the remanent stored energy in a storage battery for use on an electric-powered vehicle, and an apparatus for warning of a reduction in the remanent stored energy in such a storage battery.
2. Description of the Prior Art
Engine-powered vehicles and recently developed electric-powered vehicles generally have a storage battery such as a lead storage battery as an electric power source. Since the storage battery must store a necessary amount of electric energy at all times to enable the vehicle to run, it is important to detect the remanent stored energy in the storage battery for the driver to recognize the same.
On the engine-powered vehicles, while the electric energy stored in the storage battery is somewhat self-discharged, the storage battery is charged by an alternator while the vehicle is running, i.e., while the engine is in operation. Therefore, the remanent stored energy in the storage battery does not need to be accurately detected, but only a relatively rough estimate of the remanent stored energy will be sufficient.
While the electric-powered vehicles are running, however, the electric energy stored in the storage battery is consumed by the motor and other electric devices on the vehicle, and the storage battery is not charged except upon regenerative braking. When the electric-powered vehicles are parked, the the electric energy stored in the storage battery is self-discharged. Consequently, it is necessary to detect the remanent stored energy in the battery highly accurately so that the driver can recognize the remaining distance the vehicle can travel with the remanent stored energy or can schedule the re-charging of the battery.
There have been proposed various methods of detecting the remanent stored energy in a storage battery. According to one process, the remanent stored energy in a storage battery is detected by detecting a voltage across the battery. Another method detects the specific gravity of the electrolyte of the battery to determine the remanent stored energy in the battery. In still another process, the integrated value of a current flowing between battery terminals per unit time is measured as the amount of electric energy which is consumed from the battery, and the detected amount of consumed electric energy is deducted from the initial amount of stored electric energy, thereby detecting the remanent stored energy in the battery. It is also known to combine these methods to determine the remanent stored energy in a storage battery.
Generally, the actual remanent stored energy in a storage battery is affected by various factors including, for example, the voltage across the battery, the specific gravity of the electrolyte, the integrated value of the current flowing between the battery terminals, the temperature of the battery, the magnitude of a discharging current flowing when the battery is discharged, the number of times that the battery has been discharged, the temperature at the time the battery is charged, and the amount of electric energy that can be charged at one time.
If it is attempted to detect the remanent stored energy in a storage battery based on limited parameters, such as the voltage across the battery, among the above numerous factors, then the remanent stored energy cannot accurately be detected, and the detected energy may sometimes differ greatly from the actual remanent stored energy because of the other factors.
Particularly, the voltage across the battery and the specific gravity of the electrolyte tend to vary to a large extent depending on the running condition of the vehicle, i.e., acceleration or deceleration. If these two factors are relied upon to detect the remanent stored energy, then it is highly difficult to accurately determine the remanent stored energy.
In view of the above considerations, it would be most preferable to provide data indicating the energy storage characteristics of a vehicle-mounted battery as a function of variables composed of all possible factors and to determine the remanent stored energy based on the data. Inasmuch as the factors that affect the remanent stored energy are intricately related to each other, the data would not easily be produced, and the number of items of the data would be too enormous to be practical.
Storage batteries can restore their initial performance if charged by an external power supply at suitable times. On electric-powered vehicles, however, the electric energy stored in the battery is consumed by an electric motor which is a main power source for driving the vehicle, and any remanent stored energy in the battery is liable to be easily reduced quickly. A large and quick reduction in the remanent stored energy is responsible for shortening the service life of the battery, resulting in a reduction in the charging efficiency. The battery cannot be charged up to an initial level of energy that the battery was initially capable of storing when charged. If an electric-powered vehicle is parked for a long time with a battery having a reduced remanent stored energy, then the remanent stored energy is further reduced because the battery is self-discharged while the vehicle is being parked. Sometimes, the remanent stored energy in the battery becomes too low to get the vehicle started after parking.
The electric-powered vehicles should preferably be equipped with some means for making the driver recognize a reduction in the stored battery energy and prompting the driver to charge the battery early. Preferably, the driver should recognize a reduction in the stored battery energy when the driver gets out of the vehicle after parking the vehicle, so that the driver can take action to have the battery charged.
One example of such means for making the driver recognize a need for charging the battery on electric-powered vehicles is a remanent battery energy meter which corresponding to the fuel meter of an engine-powered vehicle. The remanent battery energy meter comprises lamps for optically indicating messages meaning "NO BATTERY CHARGING REQUIRED", "BATTERY CHARGING REQUIRED", "RUNNING TROUBLE", etc.
Since the optical indications on the remanent battery energy meter are only visually effective, the driver may not fully recognize a need for charging the battery when it really needs to be charged. This is because the driver tends to think that the electric-powered vehicle can start again if any amount of electric energy remains stored in the battery, just like the fuel in the fuel tank of an engine-powered vehicle, and also because the driver often fails to confirm the remanent battery energy meter when he gets out of the vehicle.
Therefore, there has been a demand for reliably letting the driver, when the remanent battery energy is lowered a certain extent, recognize a need for charging the battery before the driver gets out of and leaves the vehicle.